Intra prediction for square and non-square blocks in video compression

ABSTRACT

A method for video decoding is provided. For a current block, whether an angular intra prediction mode for the current block is a wide angle mode that is in a direction outside of a range of directions that spans a bottom left diagonal direction and a top right diagonal direction of the current block is determined. Based on the angular intra prediction mode being determined as the wide angle mode, an intra smooth filter is enabled, the enabled intra smooth filter is applied to blocks neighboring the current block to generate filtered blocks, and intra prediction is performed based on the filtered blocks to decode the current block.

INCORPORATION BY REFERENCE

This present application is a continuation of U.S. application Ser. No.18/070,314, “INTRA PREDICTION FOR SQUARE AND NON-SQUARE BLOCKS IN VIDEOCOMPRESSION” filed on Nov. 28, 2022, which is a continuation of U.S.application Ser. No. 17/450,791, “METHOD AND APPARATUS FOR INTRAPREDICTION FOR NON-SQUARE BLOCKS IN VIDEO COMPRESSION” filed on Oct. 13,2021, now U.S. Pat. No. 11,558,603, which claims priority to U.S.application Ser. No. 16/752,342, “METHOD AND APPARATUS FOR INTRAPREDICTION FOR NON-SQUARE BLOCKS IN VIDEO COMPRESSION” filed on Jan. 24,2020, now U.S. Pat. No. 11,240,490, which is a continuation of U.S.application Ser. No. 16/147,533, “METHOD AND APPARATUS FOR INTRAPREDICTION FOR NON-SQUARE BLOCKS IN VIDEO COMPRESSION” filed on Sep. 28,2018, now U.S. Pat. No. 10,567,752, which claims the benefit of priorityto U.S. Provisional Application No. 62/693,046, “INTRA PREDICTION FORSQUARE AND NON-SQUARE BLOCKS IN VIDEO COMPRESSION” filed on Jul. 2,2018, each of which is incorporated by reference herein in its entirety.

TECHNICAL FIELD

The present disclosure describes embodiments generally related to videocoding.

BACKGROUND

The background description provided herein is for the purpose ofgenerally presenting the context of the disclosure. Work of thepresently named inventors, to the extent the work is described in thisbackground section, as well as aspects of the description that may nototherwise qualify as prior art at the time of filing, are neitherexpressly nor impliedly admitted as prior art against the presentdisclosure.

Video coding and decoding can be performed using inter-pictureprediction with motion compensation. Uncompressed digital video caninclude a series of pictures, each picture having a spatial dimensionof, for example, 1920×1080 luminance samples and associated chrominancesamples. The series of pictures can have a fixed or variable picturerate (informally also known as frame rate), of, for example 60 picturesper second or 60 Hz. Uncompressed video has significant bitraterequirements. For example, 1080 p60 4:2:0 video at 8 bit per sample(1920×1080 luminance sample resolution at 60 Hz frame rate) requiresclose to 1.5 Gbit/s bandwidth. An hour of such video requires more than600 GByte of storage space.

One purpose of video coding and decoding can be the reduction ofredundancy in the input video signal, through compression. Compressioncan help reduce aforementioned bandwidth or storage space requirements,in some cases by two orders of magnitude or more. Both lossless andlossy compression, as well as a combination thereof can be employed.Lossless compression refers to techniques where an exact copy of theoriginal signal can be reconstructed from the compressed originalsignal. When using lossy compression, the reconstructed signal may notbe identical to the original signal, but the distortion between originaland reconstructed signal is small enough to make the reconstructedsignal useful for the intended application. In the case of video, lossycompression is widely employed. The amount of distortion tolerateddepends on the application; for example, users of certain consumerstreaming applications may tolerate higher distortion than users oftelevision contribution applications. The compression ratio achievablecan reflect that: higher allowable/tolerable distortion can yield highercompression ratios.

A video encoder and decoder can utilize techniques from several broadcategories, including, for example, motion compensation, transform,quantization, and entropy coding.

Video codec technologies can include techniques known as intra coding.In Intra coding, sample values are represented without reference tosamples or other data from previously reconstructed reference pictures.In some video codecs, the picture is spatially subdivided into blocks ofsamples. When all blocks of samples are coded in intra mode, thatpicture can be an intra picture. Intra pictures and their derivationssuch as independent decoder refresh pictures, can be used to reset thedecoder state and can, therefore, be used in as the first picture in acoded video bitstream and a video session, or as a still image. Thesamples of an intra block can be exposed to a transform, and thetransform coefficients can be quantized before entropy coding. Intraprediction can be a technique that minimizes sample values in thepre-transform domain. In some cases, the smaller the DC value after atransform is, and the smaller the AC coefficients are, the fewer bitsare required at a given quantization step size to represent the blockafter entropy coding.

Traditional intra coding such as known from, for example MPEG-2generation coding technologies does not use intra prediction. However,some newer video compression technologies include techniques thatattempt, from, for example, surrounding sample data and/or metadataobtained during the encoding/decoding of spatially neighboring, andpreceding in decoding order, blocks of data. Such techniques arehenceforth called “intra prediction” techniques. Note that in at leastsome cases, intra prediction is only using reference data from thecurrent picture under reconstruction and not from reference pictures.

There can be many different forms of intra prediction. When more thanone of such techniques can be used in a given video coding technology,the technique in use can be coded in an intra prediction mode. Incertain cases, modes can have submodes and/or parameters, and those canbe coded individually or included in the mode codeword. Which codewordto use for a given mode/submode/parameter combination can have an impactin the coding efficiency gain through intra prediction, and so can theentropy coding technology used to translate the codewords into abitstream.

A certain mode of intra prediction was introduced with H.264, refined inH.265, and further refined in newer coding technologies such as jointexploration model (JEM), versatile video coding (VVC), benchmark set(BMS). A predictor block can be formed using neighboring samples valuesbelonging to already available samples. Sample values of neighboringsamples are copied into the predictor block according to a direction. Areference to the direction in use can be coded in the bitstream or mayitself be predicted.

The number of possible directions has increased as video codingtechnology developed. In H.264 (year 2003), nine different directioncould be represented. That increased to 33 in H.265 (year 2013), andJEM/VVC/BMS, at the time of disclosure, can support up to 65 directions.Experiments have been conducted to identify the most likely directions,and certain techniques in the entropy coding are used to represent thoselikely directions in a small number of bits, accepting a certain penaltyfor less likely directions. Further, the directions themselves can besometimes be predicted from neighboring directions used in neighboring,already decoded, blocks.

The mapping of an intra prediction directions bits in the coded videobitstream that represent the direction can be different form videocoding technology to video coding technology; and can range, forexample, from simple direct mappings of prediction direction to intraprediction mode to codewords, to complex adaptive schemes involving mostprobably modes and similar techniques. A person skilled in the art isreadily familiar with those techniques. In all cases, however, there canbe certain directions that are statistically less likely to occur invideo content than certain other directions. As the goal of videocompression is the reduction of redundancy, those less likely directionswill, in a well working video coding technology, be represented by alarger number of bits than more likely directions.

Conventional intra prediction does not take into account wide angulardirections that could be useful for non-square blocks. Furthermore, inconventional intra prediction, all intra prediction modes share a sameintra smoothing filter, which may not be efficient for wide angles.Additionally, for the luma and chroma component, the neighbouringsamples used for intra prediction sample generations are filtered beforethe generation process. The filtering is controlled by a given intraprediction mode and block size, and the average of a width and height isused to denote the block size. However, the intra prediction may beperformed from the above side or left side, and thus, it is not optimalto always use the average of the width and height of the block as theblock size.

SUMMARY

According to an embodiment of the present disclosure, there is provideda method for video decoding includes determining, for a current blockthat is a non-square block, whether an angular intra prediction mode forthe current block is a wide angle mode that is in a direction outside ofa range of directions that spans a bottom left diagonal direction andtop right diagonal direction of the current block; in response todetermining that the angular intra prediction mode is the wide anglemode, determining whether a condition to apply an intra smoothing filterto blocks neighboring the current block is satisfied; in response todetermining that the condition is satisfied, applying the intrasmoothing filter to the blocks neighboring the current block; andperforming intra prediction based on the filtered blocks to obtain acharacteristic value for the current block.

According to an embodiment of the present disclosure, there is provideda video decoder for video decoding that includes processing circuitryconfigured to determine, for a current block that is a non-square block,whether an angular intra prediction mode for the current block is a wideangle mode that is in a direction outside of a range of directions thatspans a bottom left diagonal direction and top right diagonal directionof the current block, in response to determining that the angular intraprediction mode is the wide angle mode, determine whether a condition toapply an intra smoothing filter to blocks neighboring the current blockis satisfied, in response to determining that the condition issatisfied, applying the intra smoothing filter to the blocks neighboringthe current block, and perform intra prediction based on the filteredblocks to obtain a characteristic value for the current block.

According to an embodiment of the present disclosure, there is provideda non-transitory computer readable medium including instructions storedtherein, which when executed by a processor in a video decodingapparatus, causes the processor to execute a method that includesdetermining, for a current block that is a non-square block, whether anangular intra prediction mode for the current block is a wide angle modethat is in a direction outside of a range of directions that spans abottom left diagonal direction and top right diagonal direction of thecurrent block; in response to determining that the angular intraprediction mode is the wide angle mode, determining whether a conditionto apply an intra smoothing filter to blocks neighboring the currentblock is satisfied; in response to determining that the condition issatisfied, applying the intra smoothing filter to the blocks neighboringthe current block; and performing intra prediction based on the filteredblocks to obtain a characteristic value for the current block.

Aspects of the disclosure also provide a non-transitorycomputer-readable medium storing instructions which when executed by acomputer for video decoding cause the computer to perform the method forvideo coding.

BRIEF DESCRIPTION OF THE DRAWINGS

Further features, the nature, and various advantages of the disclosedsubject matter will be more apparent from the following detaileddescription and the accompanying drawings in which:

FIG. 1 is a schematic illustration of a simplified block diagram of acommunication system (100) in accordance with an embodiment.

FIG. 2 is a schematic illustration of a simplified block diagram of acommunication system (200) in accordance with an embodiment.

FIG. 3 is a schematic illustration of a simplified block diagram of adecoder in accordance with an embodiment.

FIG. 4 is a schematic illustration of a simplified block diagram of anencoder in accordance with an embodiment.

FIG. 5 shows a block diagram of an encoder in accordance with anotherembodiment.

FIG. 6 shows a block diagram of a decoder in accordance with anotherembodiment.

FIG. 7 is a schematic illustration of exemplary intra prediction modes.

FIG. 8(A) and (B) illustrate the various angular modes for 35 predictionmodes.

FIG. 9(A) and (B) illustrate the various angular modes for 67 predictionmodes.

FIG. 10 illustrates exemplary wide angular prediction modes.

FIG. 11 illustrates an embodiment of a process performed by an encoderor decoder.

FIG. 12 illustrates an embodiment of a process performed by an encoderor decoder.

FIG. 13 is a schematic illustration of a computer system in accordancewith an embodiment.

DETAILED DESCRIPTION OF EMBODIMENTS

FIG. 1 illustrates a simplified block diagram of a communication system(100) according to an embodiment of the present disclosure. Thecommunication system (100) includes a plurality of terminal devices thatcan communicate with each other, via, for example, a network (150). Forexample, the communication system (100) includes a first pair ofterminal devices (110) and (120) interconnected via the network (150).In the FIG. 1 example, the first pair of terminal devices (110) and(120) performs unidirectional transmission of data. For example, theterminal device (110) may code video data (e.g., a stream of videopictures that are captured by the terminal device (110)) fortransmission to the other terminal device (120) via the network (150).The encoded video data can be transmitted in the form of one or morecoded video bitstreams. The terminal device (120) may receive the codedvideo data from the network (150), decode the coded video data torecover the video pictures and display video pictures according to therecovered video data. Unidirectional data transmission may be common inmedia serving applications and the like.

In another example, the communication system (100) includes a secondpair of terminal devices (130) and (140) that performs bidirectionaltransmission of coded video data that may occur, for example, duringvideoconferencing. For bidirectional transmission of data, in anexample, each terminal device of the terminal devices (130) and (140)may code video data (e.g., a stream of video pictures that are capturedby the terminal device) for transmission to the other terminal device ofthe terminal devices (130) and (140) via the network (150). Eachterminal device of the terminal devices (130) and (140) also may receivethe coded video data transmitted by the other terminal device of theterminal devices (130) and (140), and may decode the coded video data torecover the video pictures and may display video pictures at anaccessible display device according to the recovered video data.

In the FIG. 1 example, the terminal devices (110), (120), (130) and(140) may be illustrated as servers, personal computers and smart phonesbut the principles of the present disclosure may be not so limited.Embodiments of the present disclosure find application with laptopcomputers, tablet computers, media players and/or dedicated videoconferencing equipment. The network (150) represents any number ofnetworks that convey coded video data among the terminal devices (110),(120), (130) and (140), including for example wireline (wired) and/orwireless communication networks. The communication network (150) mayexchange data in circuit-switched and/or packet-switched channels.Representative networks include telecommunications networks, local areanetworks, wide area networks and/or the Internet. For the purposes ofthe present discussion, the architecture and topology of the network(150) may be immaterial to the operation of the present disclosureunless explained herein below.

FIG. 2 illustrates, as an example for an application for the disclosedsubject matter, the placement of a video encoder and a video decoder ina streaming environment. The disclosed subject matter can be equallyapplicable to other video enabled applications, including, for example,video conferencing, digital TV, storing of compressed video on digitalmedia including CD, DVD, memory stick and the like, and so on.

A streaming system may include a capture subsystem (213), that caninclude a video source (201), for example a digital camera, creating forexample a stream of video pictures (202) that are uncompressed. In anexample, the stream of video pictures (202) includes samples that aretaken by the digital camera. The stream of video pictures (202),depicted as a bold line to emphasize a high data volume when compared toencoded video data (204) (or coded video bitstreams), can be processedby an electronic device (220) that includes a video encoder (203)coupled to the video source (201). The video encoder (203) can includehardware, software, or a combination thereof to enable or implementaspects of the disclosed subject matter as described in more detailbelow. The encoded video data (204) (or encoded video bitstream (204)),depicted as a thin line to emphasize the lower data volume when comparedto the stream of video pictures (202), can be stored on a streamingserver (205) for future use. One or more streaming client subsystems,such as client subsystems (206) and (208) in FIG. 2 can access thestreaming server (205) to retrieve copies (207) and (209) of the encodedvideo data (204). A client subsystem (206) can include a video decoder(210), for example, in an electronic device (230). The video decoder(210) decodes the incoming copy (207) of the encoded video data andcreates an outgoing stream of video pictures (211) that can be renderedon a display (212) (e.g., display screen) or other rendering device (notdepicted). In some streaming systems, the encoded video data (204),(207), and (209) (e.g., video bitstreams) can be encoded according tocertain video coding/compression standards. Examples of those standardsinclude ITU-T Recommendation H.265. In an example, a video codingstandard under development is informally known as Versatile Video Codingor VVC. The disclosed subject matter may be used in the context of VVC.

It is noted that the electronic devices (220) and (230) can includeother components (not shown). For example, the electronic device (220)can include a video decoder (not shown) and the electronic device (230)can include a video encoder (not shown) as well.

FIG. (3) shows a block diagram of a video decoder (310) according to anembodiment of the present disclosure. The video decoder (310) can beincluded in an electronic device (330). The electronic device (330) caninclude a receiver (331) (e.g., receiving circuitry). The video decoder(310) can be used in the place of the video decoder (210) in the FIG. 2example.

The receiver (331) may receive one or more coded video sequences to bedecoded by the video decoder (310); in the same or another embodiment,one coded video sequence at a time, where the decoding of each codedvideo sequence is independent from other coded video sequences. Thecoded video sequence may be received from a channel (301), which may bea hardware/software link to a storage device which stores the encodedvideo data. The receiver (331) may receive the encoded video data withother data, for example, coded audio data and/or ancillary data streams,that may be forwarded to their respective using entities (not depicted).The receiver (331) may separate the coded video sequence from the otherdata. To combat network jitter, a buffer memory (315) may be coupled inbetween the receiver (331 and an entropy decoder/parser (320) (“parser(320)” henceforth). In certain applications, the buffer memory (315) ispart of the video decoder (310). In others, it can be outside of thevideo decoder (310) (not depicted). In still others, there can be abuffer memory (not depicted) outside of the video decoder (310), forexample to combat network jitter, and in addition another buffer memory(315) inside the video decoder (310), for example to handle playouttiming. When the receiver (331) is receiving data from a store/forwarddevice of sufficient bandwidth and controllability, or from anisosynchronous network, the buffer memory (315) may not be needed, orcan be small. For use on best effort packet networks such as theInternet, the buffer memory (315) may be required, can be comparativelylarge and can be advantageously of adaptive size, and may at leastpartially be implemented in an operating system or similar elements (notdepicted) outside of the video decoder (310).

The video decoder (310) may include the parser (320) to reconstructsymbols (321) from the coded video sequence. Categories of those symbolsinclude information used to manage operation of the video decoder (310),and potentially information to control a rendering device such as arender device (312) (e.g., a display screen) that is not an integralpart of the electronic device (330) but can be coupled to the electronicdevice (330), as was shown in FIG. 3 . The control information for therendering device(s) may be in the form of Supplementary EnhancementInformation (SEI messages) or Video Usability Information (VUI)parameter set fragments (not depicted). The parser (320) mayparse/entropy-decode the coded video sequence that is received. Thecoding of the coded video sequence can be in accordance with a videocoding technology or standard, and can follow various principles,including variable length coding, Huffman coding, arithmetic coding withor without context sensitivity, and so forth. The parser (320) mayextract from the coded video sequence, a set of subgroup parameters forat least one of the subgroups of pixels in the video decoder, based uponat least one parameter corresponding to the group. Subgroups can includeGroups of Pictures (GOPs), pictures, tiles, slices, macroblocks, CodingUnits (CUs), blocks, Transform Units (TUs), Prediction Units (PUs) andso forth. The parser (320) may also extract from the coded videosequence information such as transform coefficients, quantizer parametervalues, motion vectors, and so forth.

The parser (320) may perform entropy decoding/parsing operation on thevideo sequence received from the buffer memory (315), so as to createsymbols (321).

Reconstruction of the symbols (321) can involve multiple different unitsdepending on the type of the coded video picture or parts thereof (suchas: inter and intra picture, inter and intra block), and other factors.Which units are involved, and how, can be controlled by the subgroupcontrol information that was parsed from the coded video sequence by theparser (320). The flow of such subgroup control information between theparser (320) and the multiple units below is not depicted for clarity.

Beyond the functional blocks already mentioned, the video decoder (310)can be conceptually subdivided into a number of functional units asdescribed below. In a practical implementation operating undercommercial constraints, many of these units interact closely with eachother and can, at least partly, be integrated into each other. However,for the purpose of describing the disclosed subject matter, theconceptual subdivision into the functional units below is appropriate.

A first unit is the scaler/inverse transform unit (351). Thescaler/inverse transform unit (351) receives a quantized transformcoefficient as well as control information, including which transform touse, block size, quantization factor, quantization scaling matrices,etc. as symbol(s) (321) from the parser (320). The scaler/inversetransform unit (351) can output blocks comprising sample values, thatcan be input into aggregator (355).

In some cases, the output samples of the scaler/inverse transform (351)can pertain to an intra coded block; that is: a block that is not usingpredictive information from previously reconstructed pictures, but canuse predictive information from previously reconstructed parts of thecurrent picture. Such predictive information can be provided by an intrapicture prediction unit (352). In some cases, the intra pictureprediction unit (352) generates a block of the same size and shape ofthe block under reconstruction, using surrounding already reconstructedinformation fetched from the current picture buffer (358). The currentpicture buffer (358) buffers, for example, partly reconstructed currentpicture and/or fully reconstructed current picture. The aggregator(355), in some cases, adds, on a per sample basis, the predictioninformation the intra prediction unit (352) has generated to the outputsample information as provided by the scaler/inverse transform unit(351).

In other cases, the output samples of the scaler/inverse transform unit(351) can pertain to an inter coded, and potentially motion compensatedblock. In such a case, a motion compensation prediction unit (353) canaccess reference picture memory (357) to fetch samples used forprediction. After motion compensating the fetched samples in accordancewith the symbols (321) pertaining to the block, these samples can beadded by the aggregator (355) to the output of the scaler/inversetransform unit (351) (in this case called the residual samples orresidual signal) so as to generate output sample information. Theaddresses within the reference picture memory (357) from where themotion compensation prediction unit (353) fetches prediction samples canbe controlled by motion vectors, available to the motion compensationprediction unit (353) in the form of symbols (321) that can have, forexample X, Y, and reference picture components. Motion compensation alsocan include interpolation of sample values as fetched from the referencepicture memory (357) when sub-sample exact motion vectors are in use,motion vector prediction mechanisms, and so forth.

The output samples of the aggregator (355) can be subject to variousloop filtering techniques in the loop filter unit (356). Videocompression technologies can include in-loop filter technologies thatare controlled by parameters included in the coded video sequence (alsoreferred to as coded video bitstream) and made available to the loopfilter unit (356) as symbols (321) from the parser (320), but can alsobe responsive to meta-information obtained during the decoding ofprevious (in decoding order) parts of the coded picture or coded videosequence, as well as responsive to previously reconstructed andloop-filtered sample values.

The output of the loop filter unit (356) can be a sample stream that canbe output to the render device (312) as well as stored in the referencepicture memory (357) for use in future inter-picture prediction.

Certain coded pictures, once fully reconstructed, can be used asreference pictures for future prediction. For example, once a codedpicture corresponding to a current picture is fully reconstructed andthe coded picture has been identified as a reference picture (by, forexample, the parser (320)), the current picture buffer (358) can becomea part of the reference picture memory (357), and a fresh currentpicture buffer can be reallocated before commencing the reconstructionof the following coded picture.

The video decoder (310) may perform decoding operations according to apredetermined video compression technology in a standard, such as ITU-TRec. H.265. The coded video sequence may conform to a syntax specifiedby the video compression technology or standard being used, in the sensethat the coded video sequence adheres to both the syntax of the videocompression technology or standard and the profiles as document in thevideo compression technology or standard. Specifically, a profile canselect a certain tools as the only tools available for use under thatprofile from all the tools available in the video compression technologyor standard. Also necessary for compliance can be that the complexity ofthe coded video sequence is within bounds as defined by the level of thevideo compression technology or standard. In some cases, levels restrictthe maximum picture size, maximum frame rate, maximum reconstructionsample rate (measured in, for example megasamples per second), maximumreference picture size, and so on. Limits set by levels can, in somecases, be further restricted through Hypothetical Reference Decoder(HRD) specifications and metadata for HRD buffer management signaled inthe coded video sequence.

In an embodiment, the receiver (331) may receive additional (redundant)data with the encoded video. The additional data may be included as partof the coded video sequence(s). The additional data may be used by thevideo decoder (310) to properly decode the data and/or to moreaccurately reconstruct the original video data. Additional data can bein the form of, for example, temporal, spatial, or signal noise ratio(SNR) enhancement layers, redundant slices, redundant pictures, forwarderror correction codes, and so on.

FIG. 4 shows a block diagram of a video encoder (403) according to anembodiment of the present disclosure. The video encoder (403) isincluded in an electronic device (420). The electronic device (420)includes a transmitter (440) (e.g., transmitting circuitry). The videoencoder (403) can be used in the place of the video encoder (203) in theFIG. 2 example.

The video encoder (403) may receive video samples from a video source(401)(that is not part of the electronic device (420) in the FIG. 4example) that may capture video image(s) to be coded by the videoencoder (403). In another example, the video source (401) is a part ofthe electronic device (420).

The video source (401) may provide the source video sequence to be codedby the video encoder (403) in the form of a digital video sample streamthat can be of any suitable bit depth (for example: 8 bit, 10 bit, 12bit, . . . ), any colorspace (for example, BT.601 Y CrCB, RGB, . . . )and any suitable sampling structure (for example Y CrCb 4:2:0, Y CrCb4:4:4). In a media serving system, the video source (401) may be astorage device storing previously prepared video. In a videoconferencingsystem, the video source (401) may be a camera that captures local imageinformation as a video sequence. Video data may be provided as aplurality of individual pictures that impart motion when viewed insequence. The pictures themselves may be organized as a spatial array ofpixels, wherein each pixel can comprise one or more samples depending onthe sampling structure, color space, etc. in use. A person skilled inthe art can readily understand the relationship between pixels andsamples. The description below focusses on samples.

According to an embodiment, the video encoder (403) may code andcompress the pictures of the source video sequence into a coded videosequence (443) in real time or under any other time constraints asrequired by the application. Enforcing appropriate coding speed is onefunction of a controller (450). In some embodiments, the controller(450) controls other functional units as described below and isfunctionally coupled to the other functional units. The coupling is notdepicted for clarity. Parameters set by the controller (450) can includerate control related parameters (picture skip, quantizer, lambda valueof rate-distortion optimization techniques, . . . ), picture size, groupof pictures (GOP) layout, maximum motion vector search range, and soforth. The controller (450) can be configured to have other suitablefunctions that pertain to the video encoder (403) optimized for acertain system design.

In some embodiments, the video encoder (403) is configured to operate ina coding loop. As an oversimplified description, in an example, thecoding loop can include a source coder (430) (e.g., responsible forcreating symbols, such as a symbol stream, based on an input picture tobe coded, and a reference picture(s)), and a (local) decoder (433)embedded in the video encoder (403). The decoder (433) reconstructs thesymbols to create the sample data in a similar manner as a (remote)decoder also would create (as any compression between symbols and codedvideo bitstream is lossless in the video compression technologiesconsidered in the disclosed subject matter). The reconstructed samplestream (sample data) is input to the reference picture memory (434). Asthe decoding of a symbol stream leads to bit-exact results independentof decoder location (local or remote), the content in the referencepicture memory (434) is also bit exact between the local encoder andremote encoder. In other words, the prediction part of an encoder “sees”as reference picture samples exactly the same sample values as a decoderwould “see” when using prediction during decoding. This fundamentalprinciple of reference picture synchronicity (and resulting drift, ifsynchronicity cannot be maintained, for example because of channelerrors) is used in some related arts as well.

The operation of the “local” decoder (433) can be the same as of a“remote” decoder, such as the video decoder (310), which has alreadybeen described in detail above in conjunction with FIG. 3 . Brieflyreferring also to FIG. 3 , however, as symbols are available andencoding/decoding of symbols to a coded video sequence by an entropycoder (445) and the parser (320) can be lossless, the entropy decodingparts of the video decoder (310), including the buffer memory (315), andparser (320) may not be fully implemented in the local decoder (433).

An observation that can be made at this point is that any decodertechnology except the parsing/entropy decoding that is present in adecoder also necessarily needs to be present, in substantially identicalfunctional form, in a corresponding encoder. For this reason, thedisclosed subject matter focuses on decoder operation. The descriptionof encoder technologies can be abbreviated as they are the inverse ofthe comprehensively described decoder technologies. Only in certainareas a more detail description is required and provided below.

During operation, in some examples, the source coder (430) may performmotion compensated predictive coding, which codes an input picturepredictively with reference to one or more previously-coded picture fromthe video sequence that were designated as “reference pictures”. In thismanner, the coding engine (432) codes differences between pixel blocksof an input picture and pixel blocks of reference picture(s) that may beselected as prediction reference(s) to the input picture.

The local video decoder (433) may decode coded video data of picturesthat may be designated as reference pictures, based on symbols createdby the source coder (430). Operations of the coding engine (432) mayadvantageously be lossy processes. When the coded video data may bedecoded at a video decoder (not shown in FIG. 4 ), the reconstructedvideo sequence typically may be a replica of the source video sequencewith some errors. The local video decoder (433) replicates decodingprocesses that may be performed by the video decoder on referencepictures and may cause reconstructed reference pictures to be stored inthe reference picture cache (434). In this manner, the video encoder(403) may store copies of reconstructed reference pictures locally thathave common content as the reconstructed reference pictures that will beobtained by a far-end video decoder (absent transmission errors).

The predictor (435) may perform prediction searches for the codingengine (432). That is, for a new picture to be coded, the predictor(435) may search the reference picture memory (434) for sample data (ascandidate reference pixel blocks) or certain metadata such as referencepicture motion vectors, block shapes, and so on, that may serve as anappropriate prediction reference for the new pictures. The predictor(435) may operate on a sample block-by-pixel block basis to findappropriate prediction references. In some cases, as determined bysearch results obtained by the predictor (435), an input picture mayhave prediction references drawn from multiple reference pictures storedin the reference picture memory (434).

The controller (450) may manage coding operations of the source coder(430), including, for example, setting of parameters and subgroupparameters used for encoding the video data.

Output of all aforementioned functional units may be subjected toentropy coding in the entropy coder (445). The entropy coder (445)translates the symbols as generated by the various functional units intoa coded video sequence, by lossless compressing the symbols according totechnologies known to a person skilled in the art as, for exampleHuffman coding, variable length coding, arithmetic coding, and so forth.

The transmitter (440) may buffer the coded video sequence(s) as createdby the entropy coder (445) to prepare for transmission via acommunication channel (460), which may be a hardware/software link to astorage device which would store the encoded video data. The transmitter(440) may merge coded video data from the video coder (403) with otherdata to be transmitted, for example, coded audio data and/or ancillarydata streams (sources not shown).

The controller (450) may manage operation of the video encoder (403).During coding, the controller (450) may assign to each coded picture acertain coded picture type, which may affect the coding techniques thatmay be applied to the respective picture. For example, pictures oftenmay be assigned as one of the following picture types:

An Intra Picture (I picture) may be one that may be coded and decodedwithout using any other picture in the sequence as a source ofprediction. Some video codecs allow for different types of Intrapictures, including, for example Independent Decoder Refresh (“IDR”)Pictures. A person skilled in the art is aware of those variants of Ipictures and their respective applications and features.

A Predictive picture (P picture) may be one that may be coded anddecoded using intra prediction or inter prediction using at most onemotion vector and reference index to predict the sample values of eachblock.

A Bi-directionally Predictive Picture (B Picture) may be one that may becoded and decoded using intra prediction or inter prediction using atmost two motion vectors and reference indices to predict the samplevalues of each block. Similarly, multiple-predictive pictures can usemore than two reference pictures and associated metadata for thereconstruction of a single block.

Source pictures commonly may be subdivided spatially into a plurality ofsample blocks (for example, blocks of 4×4, 8×8, 4×8, or 16×16 sampleseach) and coded on a block-by-block basis. Blocks may be codedpredictively with reference to other (already coded) blocks asdetermined by the coding assignment applied to the blocks' respectivepictures. For example, blocks of I pictures may be codednon-predictively or they may be coded predictively with reference toalready coded blocks of the same picture (spatial prediction or intraprediction). Pixel blocks of P pictures may be coded predictively, viaspatial prediction or via temporal prediction with reference to onepreviously coded reference pictures. Blocks of B pictures may be codedpredictively, via spatial prediction or via temporal prediction withreference to one or two previously coded reference pictures.

The video encoder (403) may perform coding operations according to apredetermined video coding technology or standard, such as ITU-T Rec.H.265. In its operation, the video encoder (403) may perform variouscompression operations, including predictive coding operations thatexploit temporal and spatial redundancies in the input video sequence.The coded video data, therefore, may conform to a syntax specified bythe video coding technology or standard being used.

In an embodiment, the transmitter (440) may transmit additional datawith the encoded video. The source coder (430) may include such data aspart of the coded video sequence. Additional data may comprisetemporal/spatial/SNR enhancement layers, other forms of redundant datasuch as redundant pictures and slices, Supplementary EnhancementInformation (SEI) messages, Visual Usability Information (VUI) parameterset fragments, and so on.

A video may be captured as a plurality of source pictures (videopictures) in a temporal sequence. Intra-picture prediction (oftenabbreviated to Intra prediction) makes uses of spatial correlation in agiven picture, and inter-picture prediction makes uses of the (temporalor other) correlation between the pictures. In an example, a specificpicture under encoding/decoding, which is referred to as a currentpicture, is partitioned into blocks. When a block in the current pictureis similar to a reference block in a previously coded and still bufferedreference picture in the video, the block in the current picture can becoded by a vector that is referred to as a motion vector. The motionvector points to the reference block in the reference picture, and canhave a third dimension identifying the reference picture, in casemultiple reference pictures are in use.

In some embodiments, a bi-prediction technique can be used in theinter-picture prediction. According to the bi-prediction technique, tworeference pictures, such as a first and a second reference picture thatare both prior in decoding order to the current picture in the video(but may be in the past and future, respectively, in display order) areused. A block in the current picture can be coded by a first motionvector that points to a first reference block in the first referencepicture, and a second motion vector that points to a second referenceblock in the second reference picture. The block can be predicted by acombination of the first reference block and the second reference block.

Further, a merge mode technique can be used in the inter-pictureprediction to improve coding efficiency. In the merge mode, a block inthe current picture can inherit motion vectors of a neighboring block(e.g., that shares a boundary with the block, is disposed in a largerpartition region with the block) in the current picture.

According to some embodiments of the disclosure, predictions, such asinter-picture predictions and intra-picture predictions are performed inthe unit of blocks. For example, according to the HEVC standard, apicture in a sequence of video pictures is partitioned into coding treeunits (CTU) for compression, the CTUs in a picture have the same size,such as 64×64 pixels, 32×32 pixels, or 16×16 pixels. In general, a CTUincludes three coding tree blocks (CTBs), which are one luma CTB and twochroma CTBs. Each CTU can be recursively quadtree split into one ormultiple coding units (CUs). For example, a CTU of 64×64 pixels can besplit into one CU of 64×64 pixels, or 4 CUs of 32×32 pixels, or 16 CUsof 16×16 pixels. In an example, each CU is analyzed to determine aprediction type for the CU, such as an inter prediction type or an intraprediction type. The CU is split into one or more prediction units (PUs)depending on the temporal and/or spatial predictability. Generally, eachPU includes a luma prediction block (PB), and two chroma PBs. In anembodiment, a prediction operation in coding (encoding/decoding) isperformed in the unit of a prediction block. Using a luma predictionblock as an example of a prediction block, the prediction block includesa matrix of values (e.g., luma values) for pixels, such as 8×8 pixels,16×16 pixels, 8×16 pixels, 16×8 pixels and the like.

FIG. 5 shows a diagram of a video encoder (503) according to anotherembodiment of the disclosure. The video encoder (503) is configured toreceive a processing block (e.g., a prediction block) of sample valueswithin a current video picture in a sequence of video pictures, andencode the processing block into a coded picture that is part of a codedvideo sequence. In an example, the video encoder (503) is used in theplace of the video encoder (203) in the FIG. 2 example.

In an HEVC example, the video encoder (503) receives a matrix of samplevalues for a processing block, such as a prediction block of 8×8samples, and the like. The video encoder (503) determines whether theprocessing block is best coded using intra mode, inter mode, orbi-prediction mode using, for example, rate-distortion optimization.When the processing block is to be coded in intra mode, the videoencoder (503) may use an intra prediction technique to encode theprocessing block into the coded picture; and when the processing blockis to be coded in inter mode or bi-prediction mode, the video encoder(503) may use an inter prediction or bi-prediction technique,respectively, to encode the processing block into the coded picture. Incertain video coding technologies, merge mode can be an inter pictureprediction submode where the motion vector is derived from one or moremotion vector predictors without the benefit of a coded motion vectorcomponent outside the predictors. In certain other video codingtechnologies, a motion vector component applicable to the subject blockmay be present. In an example, the video encoder (503) includes othercomponents, such as a mode decision module (not shown) to determine themode of the processing blocks.

In the FIG. 5 example, the video encoder (503) includes the interencoder (530), an intra encoder (522), a residue calculator (523), aswitch (526), a residue encoder (524), a general controller (521) and anentropy encoder (525) coupled together as shown in FIG. 5 .

The inter encoder (530) is configured to receive the samples of thecurrent block (e.g., a processing block), compare the block to one ormore reference blocks in reference pictures (e.g., blocks in previouspictures and later pictures), generate inter prediction information(e.g., description of redundant information according to inter encodingtechnique, motion vectors, merge mode information), and calculate interprediction results (e.g., predicted block) based on the inter predictioninformation using any suitable technique.

The intra encoder (522) is configured to receive the samples of thecurrent block (e.g., a processing block), in some cases compare theblock to blocks already coded in the same picture, generate quantizedcoefficients after transform and, in some cases also intra predictioninformation (e.g., an intra prediction direction information accordingto one or more intra encoding techniques).

The general controller (521) is configured to determine general controldata and control other components of the video encoder (503) based onthe general control data. In an example, the general controller (521)determines the mode of the block, and provides a control signal to theswitch (526) based on the mode. For example, when the mode is the intra,the general controller (521) controls the switch (526) to select theintra mode result for use by the residue calculator (523), and controlsthe entropy encoder (525) to select the intra prediction information andinclude the intra prediction information in the bitstream; and when themode is the inter mode, the general controller (521) controls the switch(526) to select the inter prediction result for use by the residuecalculator (523), and controls the entropy encoder (525) to select theinter prediction information and include the inter predictioninformation in the bitstream.

The residue calculator (523) is configured to calculate a difference(residue data) between the received block and prediction resultsselected from the intra encoder (522) or the inter encoder (530). Theresidue encoder (524) is configured to operate based on the residue datato encode the residue data to generate the transform coefficients. In anexample, the residue encoder (524) is configured to convert the residuedata in the frequency domain, and generate the transform coefficients.The transform coefficients are then subject to quantization processingto obtain quantized transform coefficients.

The entropy encoder (525) is configured to format the bitstream toinclude the encoded block. The entropy encoder (525) is configured toinclude various information according to a suitable standard, such asHEVC standard. In an example, the entropy encoder (525) is configured toinclude the general control data, the selected prediction information(e.g., intra prediction information or inter prediction information),the residue information, and other suitable information in thebitstream. Note that, according to the disclosed subject matter, whencoding a block in the merge submode of either inter mode orbi-prediction mode, there is no residue information.

FIG. 6 shows a diagram of a video decoder (610) according to anotherembodiment of the disclosure. The video decoder (610) is configured toreceive a coded pictures that are part of a coded video sequence, anddecode the coded picture to generate a reconstructed picture. In anexample, the video decoder (610) is used in the place of the videodecoder (210) in the FIG. 2 example.

In the FIG. 6 example, the video decoder (610) includes an entropydecoder (671), an inter decoder (680), a residue decoder (673), areconstruction module (674), and an intra decoder (672) coupled togetheras shown in FIG. 6 .

The entropy decoder (671) can be configured to reconstruct, from thecoded picture, certain symbols that represent the syntax elements ofwhich the coded picture is made up. Such symbols can include, forexample, the mode in which a block is coded (such as, for example,intra, inter, b-predicted, the latter two in merge submode or anothersubmode), prediction information (such as, for example, intra predictioninformation or inter prediction information) that can identify certainsample or metadata that is used for prediction by the intra decoder(672) or the inter decoder (680) respectively residual information inthe form of, for example, quantized transform coefficients, and thelike. In an example, when the prediction mode is inter or bi-predictedmode, the inter prediction information is provided to the inter decoder(680); and when the prediction type is the intra prediction type, theintra prediction information is provided to the intra decoder (672). Theresidual information can be subject to inverse quantization and isprovided to the residue decoder (673).

The inter decoder (680) is configured to receive the inter predictioninformation, and generate inter prediction results based on the interprediction information.

The intra decoder (672) is configured to receive the intra predictioninformation, and generate prediction results based on the intraprediction information.

The residue decoder (673) is configured to perform inverse quantizationto extract de-quantized transform coefficients, and process thede-quantized transform coefficients to convert the residual from thefrequency domain to the spatial domain. The residue decoder (673) mayalso require certain control information (to include the QuantizerParameter QP), and that information may be provided by the entropydecoder (671) (datapath not depicted as this may be low volume controlinformation only).

The reconstruction module (674) is configured to combine, in the spatialdomain, the residual as output by the residue decoder (673) and theprediction results (as output by the inter or intra prediction modulesas the case may be) to form a reconstructed block, that may be part ofthe reconstructed picture, which in turn may be part of thereconstructed video. It is noted that other suitable operations, such asa deblocking operation and the like, can be performed to improve thevisual quality.

It is noted that the video encoders (203), (403) and (503), and thevideo decoders (210), (310) and (610) can be implemented using anysuitable technique. In an embodiment, the video encoders (203), (403)and (503), and the video decoders (210), (310) and (610) can beimplemented using one or more integrated circuits. In anotherembodiment, the video encoders (203), (403) and (403), and the videodecoders (210), (310) and (610) can be implemented using one or moreprocessors that execute software instructions.

FIG. 7 illustrates an embodiment of exemplary angular modes used forintra prediction. In FIG. 7 , depicted in the lower right is an exampleof nine prediction directions, which may be from H.265's 35 possibleprediction directions. The point where the arrows converge (701)represents the sample being predicted. The arrows represent thedirection from which the sample is being predicted. For example, arrow(702) indicates that sample (701) is predicted from a sample or samplesto the upper right, at a 45 degree angle from the horizontal axis.Similarly, arrow (703) indicates that sample (701) is predicted from asample or samples to the lower left of sample (701), in a 22.5 degreeangle from the horizontal axis.

Still referring to FIG. 7 , on the top left there is depicted a squareblock (704) of 4×4 samples (indicated by a dashed, boldface line). Thesquare block (704) includes 16 samples, each labelled with an “S”, itsposition in the Y dimension (e.g., row index), and its position in the Xdimension (e.g., column index). For example, sample S21 is the secondsample in the Y dimension (from the top) and the first (from the left)sample in the X dimension. Similarly, sample S44 is the fourth sample inblock (704) in both the Y and X dimension. As the block is 4×4 samplesin size, S44 is at the bottom right. Further shown are referencesamples, that follow a similar numbering scheme. A reference sample islabelled with an R, its Y position (e.g., row index) and X position(column index) relative to block (704). Intra picture prediction canwork by copying reference sample values from the neighboring samples asappropriated by the signaled prediction direction. For example, assumethe coded video bitstream includes signaling that, for this block,indicates a prediction direction consistent with arrow (702)—that is,samples are predicted from prediction sample or samples to the upperright, at a 45 degree angle from the horizontal. In that case, samplesS41, S32, S23, and S14 are predicted from same R05. Sample S44 is thenpredicted from R08.

In certain cases, the values of multiple reference samples may becombined, for example through interpolation, in order to calculate areference sample; especially when the directions are not evenlydivisible by 45 degrees.

FIG. 8(A) and (B) illustrate an embodiment of 35 total intra predictionmodes including 33 angular modes. Mode 0 is the INTRA_PLANAR mode, andmode 1 is the INTRA_DC mode. Furthermore, Modes 2-34 represent the intraangular modes. As understood by one of ordinary skill in the art, thebottom-left diagonal mode is mode 2, the top-right diagonal mode is mode34, mode 10 is the horizontal angular mode, and mode 26 is the verticalmode.

FIG. 9(A) and (B) illustrate an embodiment of 67 total intra predictionmodes including 65 angular modes. Mode 0 is the INTRA_PLANAR mode, andmode 1 is the INTRA_DC mode. Furthermore, Modes 2-66 represent intraangular modes INTRA_ANGULAR2-INTRA_ANGULAR66, respectively. Asunderstood by one of ordinary skill in the art, mode 18 is thehorizontal mode, and mode 50 is the vertical mode.

FIG. 10 illustrates a block 1000 with wide angular modes. For example,in FIG. modes 2 to 34 are intra prediction modes 180 degrees apartbetween a top-right and bottom-left diagonal direction, which may becalled conventional intra prediction modes. The block 1000 may furtherinclude wide angular intra prediction modes that are beyond the range ofprediction directions covered by conventional intra prediction modes.For example, modes 35 and 36 in block 1000 are wide angular intraprediction modes. Each wide angular intra prediction mode may beassociated with one conventional intra prediction mode, where eachwide-angular intra prediction mode and its associated intra predictionmode capture the same direction, but using the reference samples atopposite sides (left column or top row). The wide angular intraprediction mode and associated conventional intra prediction mode may bespaced apart from each other by 180 degrees. For example, wide angularintra prediction mode 35 is associated with conventional angular intraprediction mode 3. Similarly, wide angular intra prediction mode 36 isassociated with conventional intra prediction mode 4.

According to some embodiments, the wide angular intra prediction modemay be signaled by sending a 1-bit flag for those associated directionsthat have an available wide angle “flip mode.” For example, in FIG. 10 ,mode 3 and mode 4 would have flags indicating whether to use theindicated conventional intra prediction mode or flipped wide angulardirection mode 35 and mode 36, respectively.

In some embodiments, when a block has 65 angular intra prediction modes,the availability of the new modes may be limited to the 10 directionalmodes closest to the 45-degree diagonal top-right mode (i.e., mode 34when 35 conventional intra modes are applied) and bottom-left mode(i.e., mode 2 when 35 conventional intra modes are applied). The sampleprediction process disclosed in the HEVC standard or VVC standard may beused.

According to some embodiments, for the luma component, the neighboringsamples used for intra prediction sample generations are filtered beforethe generation process. The filtering may be controlled by the givenintra prediction mode and transform block size. In some embodiments, ifthe intra prediction mode is DC or the transform block size is equal to4×4, neighboring samples are not filtered. In some embodiments, if thedistance between the given intra prediction mode and vertical mode (orhorizontal mode) is larger than a predefined threshold, the filteringprocess is enabled. The threshold may depend on the width (or height) ofa block when intra prediction is applied on square blocks. In someembodiments, the threshold depends on the area size of a block, i.e.,(log₂(width)+log₂(height))>>1.

According to some embodiments, whether intra smoothing filter is enabledfor wide angular modes may be dependent on the block size. In someembodiments, intra smoothing filtering is always enabled for wide angleswith all block sizes. For example, a parameter associated with a blockmay indicate that intra smoothing filtering may be applied regardless ofblock size. In some embodiments, intra smooth filtering is enabled forwide angle with certain block sizes and disabled for other block sizes.For example, when a block size of a current block is larger than orequal to a predetermined block size threshold (e.g., 32), the intrasmooth filter is disabled for wide angles. If the block size is lessthan the predetermined block size threshold, the intra smooth filteringis enabled. In some embodiments, the block size of a current block isdetermined by a width or height of the current block. In someembodiments, the block size of the current block is determined by anaverage of the width and height of the current block.

According to some embodiments, a coding tool X has a selection ofseveral modes including an intra prediction mode. When a wide angularintra prediction mode is used, and the behavior of mode selection forthe coding tool X is not defined or the coding tool X does not support awide angle intra prediction mode, the wide angle intra prediction modemay be mapped to one of the conventional intra prediction modes. Themapped conventional intra prediction mode may be used to decide theselection of mode for the coding tool X. In some embodiments, a wideangular intra prediction mode is mapped to its associated conventionalintra prediction mode. For example, the wide angular intra predictionmode 35 is mapped to conventional intra prediction mode 3. Similarly,the wide angular intra prediction mode 36 is mapped to conventionalintra prediction mode 4.

In some embodiments, the wide angular intra prediction mode is mapped toa nearest conventional intra prediction mode. For example, wide angularintra prediction modes 35, 36, 37, and 38 may be mapped to conventionalintra prediction mode 34, and wide angular intra prediction modes −1,−2, −3, and −4 may be mapped to conventional intra prediction mode 2. Inanother example, when there are 65 conventional angular intra predictionmodes, wide angular intra prediction modes 67 to 74 may be mapped toconventional intra prediction mode 66, and wide angular intra predictionmodes −1 to −8 may be mapped to conventional intra prediction mode 2.

In some embodiments, the coding tool X may be a tool such as, but notlimited to, Position Dependent Prediction Combination (PDPC), AdaptiveMultiple Transform (AMT), Non-Separable Secondary Transform (NSST), andPrediction dependent transform.

FIG. 11 illustrates an embodiment of a process performed by an encoderor decoder such as intra encoder 522 or intra decoder 672, respectively.The process illustrated in FIG. 11 may be performed for non-squareblocks. The process may start at step S1100 where it is determinedwhether an angular intra prediction mode for the current block is a wideangle mode. As discussed above, the wide angle mode includes directionsoutside of a range of directions that spans a bottom left diagonaldirection and top right diagonal direction of the current block. Forexample, when there are 33 conventional angular intra prediction modes,an angular mode number greater than 34 or a negative angular mode numberindicates that the angular intra prediction mode for the current blockis the wide angle mode. Similarly, when there are 65 conventionalangular intra prediction modes, an angular mode number greater than 66or a negative angular mode number indicates that the angular intraprediction mode for the current block is the wide angle mode. If theangular intra prediction mode is not a wide angle mode, the processproceeds to step S1102 (“No”) to perform intra prediction for thecurrent block based on a conventional intra prediction mode.

If the angular intra prediction mode is the wide angle mode, the processproceeds to step S1104 (“Yes”), to determine whether a condition toapply an intra smoothing filter to blocks neighboring the current blockis satisfied. For example, the condition may be satisfied if a parameterassociated with enabling intra smooth filtering indicates that intrasmooth filtering is applied regardless of block size. In anotherexample, the condition may be satisfied when a block size of the currentblock is greater than a predetermined block size threshold, where theblock size may be determined in accordance with a height, width, or anaverage of the height and width of the current block.

If the condition to apply intra smooth filtering is not satisfied, theprocess proceeds to step S1106 (“No”) where intra prediction isperformed based on unfiltered blocks to obtain a characteristic valuefor the current block. However, if the condition to apply intra soothfiltering is satisfied, the process proceeds from step S1104 to stepS1108 (“Yes”) where the intra smoothing filter is applied to the blocksneighboring the current block. The process proceeds to step S1110 whereintra prediction based on the filtered blocks is performed to obtain acharacteristic for the current block is performed .

FIG. 12 illustrates an embodiment of a process performed by an encoderor decoder such as intra encoder 522 or intra decoder 672, respectively.The process may start at step S1200 where it is determined whether acoding tool that performs intra prediction supports the wide angle mode.If the coding tool supports the wide angle mode, the process proceeds tostep S1202 (“Yes”) where intra prediction is performed using the wideangle mode. However, if the coding tool does not support the wide anglemode, the process proceeds to step S1204 (“No”), where the angular intraprediction mode is changed to an intra prediction mode included in therange of directions that spans the bottom left diagonal direction andtop right diagonal direction of the current block. For example, if theangular intra prediction mode is a wide angle mode, the wide angle modeis mapped to a corresponding conventional intra prediction associatedwith the wide angle mode, or the wide angle mode is mapped to thenearest conventional intra prediction mode.

According to some embodiments, for determining the condition for intrasmoothing filter for angular prediction modes is satisfied, if a currentintra prediction mode is a vertical-like direction (e.g., closer tovertical direction than horizontal direction, such as, mode 18-34 when35 intra modes are applied and mode 34-66 when 67 intra modes areapplied), a width of a current block is used to decide whether and whichintra smoothing filter is applied. Furthermore, if a current intraprediction is a horizontal-like direction (e.g., closer to horizontaldirection than vertical direction, such as mode 2-17 when 35 intra modesare applied, and mode 2-33 when 67 intra modes are applied), a height ofthe current is used to decide whether and which intra smoothing filteris applied.

For example, when there are 35 intra prediction modes, when the modeindex of a current angular direction is equal to or larger than 18, awidth of a current block is used to denote the current block size suchthat the sampling filtering depends only on the prediction mode andblock width. Otherwise, when the mode index of the current angulardirection is less than 18, a height of the current block is used todenote the current block size such that the sampling filtering dependsonly on the prediction mode and block height.

In another example, when there are 67 intra prediction modes, when themode index of a current angular direction is equal to or larger than 34,a width of the current block is used to denote the current block sizesuch that the sampling filtering depends only on the prediction mode andblock height. Otherwise, when the mode index of the current angulardirection is less than 34, a height of the current block is used todenote the current block size such that the sampling filtering dependsonly on the prediction mode and block height.

The following embodiments disclose example intra smooth filters.

Inputs to this process are:

-   -   the neighbouring samples p[x][y], with x=−1, y=−1 . . .        nWidth+nHeight−1 and x=0 . . . nWidth+nHeight−1, y=−1,    -   a variable nWidth specifying the transform block width.        -   a variable nHeight specifying the transform block height.

Outputs of this process are the filtered samples pF[x][y], with x=−1 ,y=−1 . . . nTbS*2−1 and x=0 . . . nTbS*2−1, y=−1.

The variable filterFlag may be derived as follows:

-   -   If the following conditions is true, filterFlag is set equal to        0:        -   predModeintra is equal to INTRA_DC.    -   Otherwise, the following applies:        -   The variable minDistVerHor is set equal to            Min(Abs(predModeintra−26), Abs(predModeintra−10)).        -   The variable nTbS may be derived as follows:            -   If predMode Intra is less than 34 and larger than                DC_IDX, nTbS is set to nHeight            -   Else ifpredMode Intra is equal to or larger than 34,                nTbS is set to nWidth            -   Else, nTbS is set to (nWidth+nHeight)>>1    -   The variable intraHorVerDistThres[nTbS] is specified in table        illustrated below.    -   The variable filterFlag is derived may be derived as follows:        -   IfminDistVerHor is greater than intraHorVerDistThres[nTbS],            filterFlag is set equal to 1.    -   Otherwise, filterFlag is set equal to 0.

The following table illustrates example values for the variableintraHorVerDistThres[nTbs] for various transform block sizes.

nTbS > 4 && nTbS > 8 && nTbS > 16 && nTbS > 32 && nTbS <= 8 nTbS <= 16nTbS <= 32 nTbS <= 64 intraHorVerDistThres[nTbS] 7 1 0 10

When filterFlag is equal to 1, the following may apply:

-   -   The variable biIntFlag is derived as follows:        -   If all of the following conditions are true, biIntFlag is            set equal to 1:            -   strong_intra_smoothing_enabled_flag is equal to 1            -   nTbS is equal to 32            -   Abs(p[−1][−1]+p[nTbS*2−1][−1]−2*p[nTbS−1][−1])<(1«(BitDepthy−5))            -   Abs(p[−1                ][−1]+p[−1][nTbS*2−1]−2*p[−1][nTbS−1])<(1«(BitDepthy−5))        -   Otherwise, bilntFlag is set equal to 0.    -   The filtering may be performed as follows:        -   If biIntFlag is equal to 1, the filtered sample values            pF[x][y] with x=−1 , y=−1 . . . 63 and x=0 . . . 63, y=−1            are derived as follows:

pF[−1][−1]=p[−1][−1]  (Eq. 1)

pF[−1][y]=((63−y)*p[−1][−1]+(y+1)*p[−1][63]+32)»6 for y=0 . . . 62  (Eq. 2)

pF[−1][63]=p[−1][63]  (Eq. 3)

pF[x][−1]=((63−x)*p[−1][−1]+(x+1)*p[63][−1]+32)»6 for x=0 . . . 62  (Eq. 4)

pF[63][−1]=p[63 ][−1]  (Eq. 5)

-   -   Otherwise (biIntFlag is equal to 0), the filtered sample values        pF[x][y] with x=−1, y=−1 . . . nTbS*2−1 and x=0 . . . nTbS*2−1,        y=−1 may be derived as follows:

pF[−1][−1]=(p[−1][9]+2*p[−1][−1]+p[0][−1]+2)»2   (Eq. 6)

pF[−1][y]=(p[−1][y+1]+2*p[−1][y]+p[−1][y−1]+2)»2 for y=0 . . . nThS*2−2  (Eq. 7))

pF[−1][nThS*2−1]=p[−1][nTbS*2−1]  (Eq. 8)

pF[x][−1]=(p[x−1][−1]+2*p[x][−1]+p[x+1][−1]+2)»2 for x=0 . . . nThS*2−2  (Eq. 9)

pF[nThS*2−1][−1]=p[nThS*2−1][−1]  (Eq. 10)

The techniques described above, can be implemented as computer softwareusing computer-readable instructions and physically stored in one ormore computer-readable media. For example, FIG. 13 shows a computersystem (1300) suitable for implementing certain embodiments of thedisclosed subject matter.

The computer software can be coded using any suitable machine code orcomputer language, that may be subject to assembly, compilation,linking, or like mechanisms to create code comprising instructions thatcan be executed directly, or through interpretation, micro-codeexecution, and the like, by one or more computer central processingunits (CPUs), Graphics Processing Units (GPUs), and the like.

The instructions can be executed on various types of computers orcomponents thereof, including, for example, personal computers, tabletcomputers, servers, smartphones, gaming devices, internet of thingsdevices, and the like.

The components shown in FIG. 13 for computer system (1300) are exemplaryin nature and are not intended to suggest any limitation as to the scopeof use or functionality of the computer software implementingembodiments of the present disclosure. Neither should the configurationof components be interpreted as having any dependency or requirementrelating to any one or combination of components illustrated in theexemplary embodiment of a computer system (1300).

Computer system (1300) may include certain human interface inputdevices. Such a human interface input device may be responsive to inputby one or more human users through, for example, tactile input (such as:keystrokes, swipes, data glove movements), audio input (such as: voice,clapping), visual input (such as: gestures), olfactory input (notdepicted). The human interface devices can also be used to capturecertain media not necessarily directly related to conscious input by ahuman, such as audio (such as: speech, music, ambient sound), images(such as: scanned images, photographic images obtain from a still imagecamera), video (such as two-dimensional video, three-dimensional videoincluding stereoscopic video).

Input human interface devices may include one or more of (only one ofeach depicted): keyboard (1301), mouse (1302), trackpad (1303), touchscreen (1310), data-glove (not shown), joystick (1305), microphone(1306), scanner (1307), camera (1308).

Computer system (1300) may also include certain human interface outputdevices. Such human interface output devices may be stimulating thesenses of one or more human users through, for example, tactile output,sound, light, and smell/taste. Such human interface output devices mayinclude tactile output devices (for example tactile feedback by thetouch-screen (1310), data-glove (not shown), or joystick (1305), butthere can also be tactile feedback devices that do not serve as inputdevices), audio output devices (such as: speakers (1309), headphones(not depicted)), visual output devices (such as screens (1310) toinclude CRT screens, LCD screens, plasma screens, OLED screens, eachwith or without touch-screen input capability, each with or withouttactile feedback capability—some of which may be capable to output twodimensional visual output or more than three dimensional output throughmeans such as stereographic output; virtual-reality glasses (notdepicted), holographic displays and smoke tanks (not depicted)), andprinters (not depicted).

Computer system (1300) can also include human accessible storage devicesand their associated media such as optical media including CD/DVD ROM/RW(1320) with CD/DVD or the like media (1321), thumb-drive (1322),removable hard drive or solid state drive (1323), legacy magnetic mediasuch as tape and floppy disc (not depicted), specialized ROM/ASIC/PLDbased devices such as security dongles (not depicted), and the like.

Those skilled in the art should also understand that term “computerreadable media” as used in connection with the presently disclosedsubject matter does not encompass transmission media, carrier waves, orother transitory signals.

Computer system (1300) can also include a network interface (1354) toone or more communication networks (1355). Networks can for example bewireless, wireline, optical. Networks can further be local, wide-area,metropolitan, vehicular and industrial, real-time, delay-tolerant, andso on. Examples of networks include local area networks such asEthernet, wireless LANs, cellular networks to include GSM, 3G, 4G, 5G,LTE and the like, TV wireline or wireless wide area digital networks toinclude cable TV, satellite TV, and terrestrial broadcast TV, vehicularand industrial to include CANBus, and so forth. Certain networkscommonly require external network interface adapters that attached tocertain general purpose data ports or peripheral buses (1349) (such as,for example USB ports of the computer system (1300)); others arecommonly integrated into the core of the computer system (1300) byattachment to a system bus as described below (for example Ethernetinterface into a PC computer system or cellular network interface into asmartphone computer system). Using any of these networks, computersystem (1300) can communicate with other entities. Such communicationcan be uni-directional, receive only (for example, broadcast TV),uni-directional send-only (for example CANbus to certain CANbusdevices), or bi-directional, for example to other computer systems usinglocal or wide area digital networks. Certain protocols and protocolstacks can be used on each of those networks and network interfaces asdescribed above.

Aforementioned human interface devices, human-accessible storagedevices, and network interfaces can be attached to a core (1340) of thecomputer system (1300).

The core (1340) can include one or more Central Processing Units (CPU)(1341), Graphics Processing Units (GPU) (1342), specialized programmableprocessing units in the form of Field Programmable Gate Areas (FPGA)(1343), hardware accelerators for certain tasks (1344), and so forth.These devices, along with Read-only memory (ROM) (1345), Random-accessmemory (1346), internal mass storage such as internal non-useraccessible hard drives, SSDs, and the like (1347), and Graphics Adapter1350 may be connected through a system bus (1348). In some computersystems, the system bus (1348) can be accessible in the form of one ormore physical plugs to enable extensions by additional CPUs, GPU, andthe like. The peripheral devices can be attached either directly to thecore's system bus (1348), or through a peripheral bus (1349).Architectures for a peripheral bus include PCI, USB, and the like.

CPUs (1341), GPUs (1342), FPGAs (1343), and accelerators (1344) canexecute certain instructions that, in combination, can make up theaforementioned computer code. That computer code can be stored in ROM(1345) or RAM (1346). Transitional data can be also be stored in RAM(1346), whereas permanent data can be stored for example, in theinternal mass storage (1347). Fast storage and retrieve to any of thememory devices can be enabled through the use of cache memory, that canbe closely associated with one or more CPU (1341), GPU (1342), massstorage (1347), ROM (1345), RAM (1346), and the like.

The computer readable media can have computer code thereon forperforming various computer-implemented operations. The media andcomputer code can be those specially designed and constructed for thepurposes of the present disclosure, or they can be of the kind wellknown and available to those having skill in the computer software arts.

As an example and not by way of limitation, the computer system havingarchitecture (1300), and specifically the core (1340) can providefunctionality as a result of processor(s) (including CPUs, GPUs, FPGA,accelerators, and the like) executing software embodied in one or moretangible, computer-readable media. Such computer-readable media can bemedia associated with user-accessible mass storage as introduced above,as well as certain storage of the core (1340) that are of non-transitorynature, such as core-internal mass storage (1347) or ROM (1345). Thesoftware implementing various embodiments of the present disclosure canbe stored in such devices and executed by core (1340). Acomputer-readable medium can include one or more memory devices orchips, according to particular needs. The software can cause the core(1340) and specifically the processors therein (including CPU, GPU,FPGA, and the like) to execute particular processes or particular partsof particular processes described herein, including defining datastructures stored in RAM (1346) and modifying such data structuresaccording to the processes defined by the software. In addition or as analternative, the computer system can provide functionality as a resultof logic hardwired or otherwise embodied in a circuit (for example:accelerator (1344)), which can operate in place of or together withsoftware to execute particular processes or particular parts ofparticular processes described herein. Reference to software canencompass logic, and vice versa, where appropriate. Reference to acomputer-readable media can encompass a circuit (such as an integratedcircuit (IC)) storing software for execution, a circuit embodying logicfor execution, or both, where appropriate. The present disclosureencompasses any suitable combination of hardware and software.

APPENDIX A: ACRONYMS

-   -   MV: Motion Vector    -   HEVC: High Efficiency Video Coding    -   SEI: Supplementary Enhancement Information    -   VUL Video Usability Information    -   GOPs: Groups of Pictures    -   TUs: Transform Units,    -   PUs: Prediction Units    -   CTUs: Coding Tree Units    -   CTBs: Coding Tree Blocks    -   PBs: Prediction Blocks    -   HRD: Hypothetical Reference Decoder    -   SNR: Signal Noise Ratio    -   CPUs: Central Processing Units    -   GPUs: Graphics Processing Units    -   CRT: Cathode Ray Tube    -   LCD: Liquid-Crystal Display    -   OLED: Organic Light-Emitting Diode    -   CD: Compact Disc    -   DVD: Digital Video Disc    -   ROM: Read-Only Memory    -   RAM: Random Access Memory    -   ASIC: Application-Specific Integrated Circuit    -   PLD: Programmable Logic Device    -   LAN: Local Area Network    -   GSM: Global System for Mobile communications    -   LTE: Long-Term Evolution    -   CANBus: Controller Area Network Bus    -   USB: Universal Serial Bus    -   PCI: Peripheral Component Interconnect    -   FPGA: Field Programmable Gate Areas    -   SSD: solid-state drive    -   IC: Integrated Circuit    -   CU: Coding Unit

While this disclosure has described several exemplary embodiments, thereare alterations, permutations, and various substitute equivalents, whichfall within the scope of the disclosure. It will thus be appreciatedthat those skilled in the art will be able to devise numerous systemsand methods which, although not explicitly shown or described herein,embody the principles of the disclosure and are thus within the spiritand scope thereof.

-   -   (1) A method for video decoding includes determining, for a        current block that is a non-square block, whether an angular        intra prediction mode for the current block is a wide angle mode        that is in a direction outside of a range of directions that        spans a bottom left diagonal direction and top right diagonal        direction of the current block; in response to determining that        the angular intra prediction mode is the wide angle mode,        determining whether a condition to apply an intra smoothing        filter to blocks neighboring the current block is satisfied; in        response to determining that the condition is satisfied,        applying the intra smoothing filter to the blocks neighboring        the current block; and performing intra prediction based on the        filtered blocks to obtain a characteristic value for the current        block.    -   (2) The method according to feature (1), in which the condition        indicates that the intra smoothing filter is applied regardless        of block size.    -   (3) The method according to feature (1) or (2), in which the        condition is satisfied in response to a determination that a        block size of the non-square block is greater than or equal to a        block size threshold.    -   (4) The method according to feature (3), in which the block size        is determined in accordance with a height, width, or an average        of the height and width of the current block.    -   (5) The method of any one of features (1)-(4), further including        determining whether a coding tool that performs the intra        prediction supports the wide angle mode; and in response to the        determination that the coding tool does not support the wide        angle mode, changing the angular prediction mode from the wide        angle mode to an intra prediction mode included in the range of        directions that spans the bottom left diagonal direction and top        right diagonal direction of the current block.    -   (6) The method of feature (5), in which the angular prediction        mode is changed to an intra prediction mode in the range of        directions having a direction that is opposite to a direction of        the wide angle mode such that the changed intra prediction mode        is 180 degrees from the wide angle mode.    -   (7) The method of feature (5), in which the angular prediction        mode is changed to an intra prediction mode in the range of        directions that is nearest to the wide angle mode.    -   (8) The method according to feature (5), in which the coding        tool is selected from a group of coding tools that includes        Position Dependent Prediction Combination (PDPC), Adaptive        Multiple Transform (AMT), Non-Separable Secondary Transform        (NSST), and Prediction dependent transform.    -   (9) A video decoder for video decoding, including processing        circuitry configured to: determine, for a current block that is        a non-square block, whether an angular intra prediction mode for        the current block is a wide angle mode that is in a direction        outside of a range of directions that spans a bottom left        diagonal direction and top right diagonal direction of the        current block, in response to determining that the angular intra        prediction mode is the wide angle mode, determine whether a        condition to apply an intra smoothing filter to blocks        neighboring the current block is satisfied, in response to        determining that the condition is satisfied, applying the intra        smoothing filter to the blocks neighboring the current block,        and perform intra prediction based on the filtered blocks to        obtain a characteristic value for the current block.    -   (10) The video decoder according to feature (9), in which the        condition indicates that the intra smoothing filter is applied        regardless of block size.    -   (11) The video decoder according to feature (9) or (10), in        which the condition is satisfied in response to a determination        that a block size of the non-square block is greater than or        equal to a block size threshold.    -   (12) The video decoder according to feature (11), in which the        block size is determined in accordance with a height, width, or        an average of the height and width of the current block.    -   (13) The video decoder according to any one of features        (9)-(12), in which the processing circuitry is further        configured to: determine whether a coding tool that performs the        intra prediction supports the wide angle mode, and in response        to the determination that the coding tool does not support the        wide angle mode, change the angular prediction mode from the        wide angle mode to an intra prediction mode included in the        range of directions that spans the bottom left diagonal        direction and top right diagonal direction of the current block.    -   (14) The video decoder according to feature (13, in which the        angular prediction mode is changed to an intra prediction mode        in the range of directions having a direction that is opposite        to a direction of the wide angle mode such that the changed        intra prediction mode is 180 degrees from the wide angle mode.    -   (15) The video decoder according to feature (14), in which the        angular prediction mode is changed to an intra prediction mode        in the range of directions that is nearest to the wide angle        mode.    -   (16) The video decoder according to feature (14), in which the        coding tool is selected from a group of coding tools that        includes Position Dependent Prediction Combination (PDPC),        Adaptive Multiple Transform (AMT), Non-Separable Secondary        Transform (NSST), and Prediction dependent transform.    -   (17) A non-transitory computer readable medium including        instructions stored therein, which when executed by a processor        in a video decoding apparatus, causes the processor to execute a        method that includes determining, for a current block that is a        non-square block, whether an angular intra prediction mode for        the current block is a wide angle mode that is in a direction        outside of a range of directions that spans a bottom left        diagonal direction and top right diagonal direction of the        current block; in response to determining that the angular intra        prediction mode is the wide angle mode, determining whether a        condition to apply an intra smoothing filter to blocks        neighboring the current block is satisfied; in response to        determining that the condition is satisfied, applying the intra        smoothing filter to the blocks neighboring the current block;        and performing intra prediction based on the filtered blocks to        obtain a characteristic value for the current block.

What is claimed is:
 1. A method for video decoding, comprising:determining, for a current block, whether an angular intra predictionmode for the current block is a wide angle mode that is in a directionoutside of a range of directions that spans a bottom left diagonaldirection and a top right diagonal direction of the current block; basedon the angular intra prediction mode being determined as the wide anglemode, enabling an intra smooth filter, applying the enabled intra smoothfilter to blocks neighboring the current block to generate filteredblocks, and performing intra prediction based on the filtered blocks todecode the current block.